#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<cstdio>
#include<algorithm>
#define debug(a) cout<<#a<<"="<<a<<endl;
using namespace std;
const int maxn=2e5+1000;
typedef long long LL;
inline LL read(){LL x=0,f=1;char ch=getchar();	while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
return x*f;}
LL a[maxn];
bool cmp(LL A,LL B){return A>B;}
bool check(LL x,LL n,LL m){
     LL sum=0;
     LL cnt=0;
     for(LL i=1;i<=n;i++){
        cnt++;
        LL div=(cnt-1)/x;
        sum+=max((LL)0,(a[i]-div));
     }
     if(sum>=m) return true;
     else return false;
}
int main(void)
{
  cin.tie(0);std::ios::sync_with_stdio(false);
  LL n,m;cin>>n>>m;
  for(LL i=1;i<=n;i++) cin>>a[i];
  sort(a+1,a+1+n,cmp);
  LL l=1;LL r=n+1;
  while(l<r){
     LL mid=(l+r)>>1;
     if(check(mid,n,m)) r=mid;
     else l=mid+1;
  }
  if(l==n+1){
    cout<<"-1"<<"\n";
  }
  else cout<<l<<"\n";
return 0;
}
